1. Field of the Invention
This invention relates to a three-dimensional image processing method and apparatus for analyzing a three-dimensional image obtained, for example, by computed tomography or magnetic resonance imaging used to make a diagnosis of an organ of a human being or processing a three-dimensional image by three-dimensional image processing for three-dimensional computer graphics, and more particularly to a three-dimensional image processing method and apparatus by which a three-dimensional image is once stored as a three-dimensional digital image into a three-dimensional memory and then the three-dimensional digital image is read out cutting it in a three-dimensional space and processed by image processing.
2. Description of the Related Art
A ray tracing voxel traversal algorithm wherein a three-dimensional space is divided into a large number of cubic voxels and a three-dimensional digital image is divided into voxels and stored into a three-dimensional memory and then a ray (3D line) is forwarded straightforwardly into the three-dimensional space to designated addresses of voxels through which the ray passes to read out the data at the addresses, and a three-dimensional image processing method which makes use of the ray tracing voxel traversal algorithm, are known, for example, from the articles published in the following documents:
1. A. FUJIMOTO, T. TANAKA and K. IWATA, "ARTS: Accelerated Ray-Tracing System", IEEE Computer Graphics & Application, 6, 4, pp. 16-26, April 1986; PA1 2. S. ZHANG, P. ZHENG and Y. AOKI, "A Fast Voxel Traversal Algorithm by LCDDA Method for Ray Tracing and Its Hardware Implementation", Journal of Theses of the Electronic Communications Information Society, D-II, Vol. J74-D-II, No. 6, pp. 708-717, June 1991; and PA1 3. N. TAYAMA, N. SHIMIZU, N. CHIBA and OTAWARA, "A Speedy Voxel-Tracing Method for Cutting Solid Display of 3.D Images", Journal of Theses of the Electronic Communications Information Society, D-II, Vol. J72-D-II, No. 9, pp. 1,332-1,340, September 1989.
Fujimoto discloses a method wherein a three-dimensional digital differential analyzer (hereinafter referred to as 3D-DDA) of ray tracing is realized using a two-dimensional digital differential analyzer (hereinafter referred to as 2D-DDA) of two orthogonal two-dimensional planes. Thang and Tayama disclose different methods wherein a technique of 2D-DDA is extended to 3D-DDA such that individual voxels are stepped forwardly and backwardly in the advancing direction of a ray to generate addresses for the voxels so that no address drop may occur.
The methods, however, require a long time to, for example, display an image three-dimensionally on a display screen or analyze an image since, when a three-dimensional digital image in a three-dimensional memory is cut and read out by a 3D-DDA, one voxel is designated for each reading cycle to repetitively read out voxel data one by one.